Means for seismic survey



May 30, 1939. Y J, P. MINTON 0,

MEANS FOR SEISMIQ SURVEY Filed Nov. 17, 1937- e Sheets-Sheet 1 iJalmzmwm May 30, 1939. J. P. MINTON MEANS FOR SEISMIC SURVEY 6Sheets-Sheet 2 Filed Nov. 17, 1957 TIME May 30, 1939. J. P. MINTON2,160,224 MEANS FOR sEIsMI'b SURVEY Filed Nov. 17, 1937 6 shegtssheet 4M14875? Ca/vmu grime/whom Guam;

May 30, 1939.

J. P. MINTON 2,160,224 I MEANS FOR SEISMIC SURVEY Filed Nov. 17, 1937 6ShetS-Shfit 5 Mum/ y 1593- J. P. MINTON 2,160,224

MEANS FOR SEISMIC SURVEY Filed Nov. 17, 1937 e Sheets-Sheet '6 l i 'L ibwumw merited av 30, I39

2,160,224 MEANS FOR SEISMIC sunvmz John P. Minton, Dallas, Tex.,assignor, by memo assignments, to Socony -Vacuum Oil Company,

Incorporated, New York, N, Y., a corporation of New York ApplicationNovember 17, 1937, Serial No- 174,969 5 on; (or, lei-0.5)

This invention relates generally to method and apparatus used inexploring the subsurface strata of the earth, and more particularly tothat phase of the art which deals with the detonation of an explosivefor the purpose of producing seismic waves; the recording of the exactinstant, at a remote point, of the detonation; the rendering moredefinite of the record which indicates the instant of detonation; theincorporation ofmeans whereby telephonic communication can be hadbetween the point where the detonation of the explosive occurs and thepoint where a seismo graphic record is being recorded; and the provisionof means for recording the time break on one trace of the seismogremwithout otherwise affecting this trace or any ofthe other traces whichmay be carried on the some seisnwgram.

Prior to this invention seismogreuh records have not indicatedaccurately the instant of detonation of the explosive that is used togenerate seismic waves, the principal reason being that no definite timebreak is present which will deflnitely marl: the exact instant ofdetonation on the seismogram. By the present invention this difficultyis obviated, and definitely and accurarely merited seismograms areobtained, by ineomcrcting in the firing and recording units of theelectric blasting circuit elements arranged as hereinafter described, sothat a definite number of derivatives are taken electricully cf theapplied voltage.

Additionally when blasters of the plungers or' generator type are usedthere is introduced into the electric circuit by the commutator brushesing the above defects and also for eliminating any cap lag indetonation.

Heretofore, due to the intensity of the current flowing in the blastingcircuits,'considerable diiliculty has been encountered in recordingrecords which are legible when electric coupling causes the time breakimpulse to be transmitted to all elements of adjacent circuits. Toovercome these difiiculties a novel circuit utilizing electrostaticallyshielded transformers has been designed.

Therefore, the primary object of this invention is the provision of amethod and means for deflnitely recording on a seismogram the exact sionof means for causing thelectric curre passing through the cap toincrease to its me; mum value relatively slowly, thereby ellminati thepossibility of any delay in detonation an the bridge wire of theelectric blasting cap 11 fused.

Still another obiect of this invention is the p1 vision of means forpreventing indications whi are similar to time-break indications frombei recorded when the blasting generator switch first closed. v I

A still further object of the invention is t provision 01- means foreliminating commutat maple from the electric circuits.

It is a further object of this invention to pr vlde means foreliminating mutual coupling 11 tween adjacent circuits and to produce abe anced system that will be free of cross-ieedlz Another object residesin the provision of mea for controlling the amplitude of the time-luresStill another'object of this invention is to pr vide means forproportioning-the voltages gel erated by speech modulations totime-break mo ulations, so that the speech modulationvoltag arerelatively low compared to those of the tim break modulation voltage.

Another object of this invention is in the pr vision of means forshortening the period of tin in which the recording instrument isaffected 1 the electrical impulse which causes the tim break.

- Other objects and advantages of the inventil will be apparent from thefollowing detailed d scription when considered in the light of t]drawings in which:

Figure 1 is a reproduction of a time-break pr duccd in the ordinarymanner.

Figure 2 is a reproduction of a time-break substantially equal amplitudeafter the first d rivative has been taken electrically, in accorl ancewith this invention.

Figure 3 is a reproduction of a time-break substantially equal amplitudealter the sccoi derivative has been taken electrically, in 500011 ancewith the teachings of this invention.

Figure 4 is an illustration of a time-brea areaaae om an actual typicalseismogram, can be recorded on the same trace only a few 'oduced "underfield conditions in thousaudths of a second after the instant ofdetomer, showing the indefiniteness of nation, and showing further howthe other traces the purpose of determining the inare not afiected bythe time-break indication. ation. Figure 25 is a similar illustration ofanother a similar illustration of another seismogram, made in accordancewith this inbich was produced in the usual vention, showing theattenuation of the time showing indefiniteness as to the break and theabsence of crossfeeding between )nation. a -traces..

an illustra'tionof an actual time-' Figure 26 is an enlargeddiagrammatic ill-us- 1 l in accordance with the teachings tration of theshot firing end of the blasting ciron showing .the definiteness withcuit.

I ascertain the instant of detona- Figure 2'? is an enlargeddiagrammatic illusilosive which produces the seismic tration'of therecording end of the blasting circuit. iillustration of anothertime-break Referring to the drawings in detail, the time- :ordance withthe teachings of this breaks shown in Figures 1, 4 and 5 illustrate ofgreater amplitude than that ordinary types of time-break which oneobtains re 6. without employing the derivator of this invena group ofcurves representing 2. tion. Figure 2 illustrates a time-break of ampli-26, he first, second, third and fourth tude equal to that shown inFigure 1 after havhe function, showing how the slope ing taken the firstderivative of the applied volte curves increases with an increasageelectrically in the manner taught by this inderivatives. vention. Theeffect of electrically taking the secdiagram illustrating a simple se0nd derivative of the applied voltage is illustrated circuit. by Figure3. Thus it can readily be seen by a diagram illustrating a simplecomparison of these curves in Figures 1, 2 and 3 ice circuit. 7 that notonly is the initial time-break rendered i'diagram illustrating a simplesemuch more definite but the period of time in which circuit. it iseffective has been reduced. This latter feaa. diagram illustratinginstantaneture enabes one to record seismic waves which urrent andvoltage, showing their originate at a point near to the recording inasimple series resistance circuit. strument, without having to contendwith the a diagram illustrating instantawave train which customarilyfollows the timecurrent and voltage, showing their break and often lastsfor a period of several huna simple series capacitance circuit. dredthsof a second. The illustrations of actual a. diagram illustratinginstantane- 1 records in Figures 24 and 25 also clearly show urrent andvoltage, showing their this advantage. It will be noted that, in thecase a simple series inductance circuit. illustrated by the upper tracein Figure 24, it was diagram illustrating a simple sepossible to obtaina definite first break within 1, resistance and capacitance cirabout.007 of a second following the'time-break (each timing line representing.01 of a second). a diagram illustrating the cur- The upper trace inFigure 25 shows that the re relationship in a circuit of the effect ofthe time-break impulse actually does die Figure15. out entirely in arelatively short time, thereby the circuit diagram for a signal makingit possible to record impulses originating 1g stage in accordance withthis at a point located a relatively short distance from ring the outputleads connected the recording Poin ;tance. In order to illustrate themeans by which a diagram showing th voltage these results are secured,reference is made tohe capacitance in 'a circuit of the the elementaryprinciples of alternating cur- Figure 17. rent circuits, which althoughwell known to one a diagram showing the manner skilled in the art, willbe given for purpose of roaches Ec with a decrease in reclearlyexplaining this invention and the results ircuit of the type shown inFigproduced in practicing the same.

The evolution or development of the derivating a circuit diagram showingtwo circuit can best be understood by first considerlg Sta es inaccordance with this ing the simple resistance, capacitance, and inductance circuits as illustrated in Figures 9, 10,

and '11 in which the. respective elements and quantities are givenconventional representative letters. The current and voltagerelationships cuirve g isbpkgted g si in these respective circuits arerepresented by fl f gi f g g isflfi g mi the instantaneous current andvoltage diagrams diagram illustrating an electrical strument embodyingthe present of Figures 12, 13, and 14. In Figure 12, the our f gig gggfigg gfgi g i g gggf rent is in phase with the voltage. Assuming a mthe current in the detonator pure capacitance circuit in Figure 13, theourad t build up over a relatively rent leads the voltage by a phaseangle of 90". ti In Figure 14, assuming a'pure inductance ciran illu tti of a seismugram cuit, the current lags behind the voltage by 2.enable commutator ripple. P se a e of 90". v an illustration of a, seismm Referring now to Figure 9, when a voltage Ea areal: on one traceshowing how, is impressed across the resistance'R a current IR rith thisinvention, seismic waves flows through R. In time relationship I and Earouses That is, the current through resistance R is proportional to theimpressed voltage Ea. However, in Figure a voltage Re is impressedacross a condenser causing a current Io to flow through the capacitance.In this case, as illustrated in Figure 13, the current lie leads thevoltage Ec by a phase angle of 9d". Here In the case'illustrated inFigure M, a voltage E1. isimpressedacross an inductance L, causing acurrent 11. to flow through the inductance. This current 1:. lags behindthevoltage Er. by a time phase angle of 90, as shown in Figure 14. Inthis case the current Izf-I/Lffiflfl the current In flowing through Lls-proportional to the integral of the impressed voltage En.

Therefore, if we have a resistance, capacitance and inductance connectedin'serles and a voltage 30 E- impressed across the entire combination,as illustrated in Figure 15, wehave 'E Ea-l-Ee-tm,

or v

- 1' d1 E- RI+ iro 2+ h the same current flowing through all theelemerits. The voltage across the inductance L will he a voltage that isproportional to the time derivative of the current I; across-0, avoltage that is proportional to the timedntegral oi the current I; andacross the R, a voltage that is proportional to thecurrent I. Thisrelationship is vectorlally illustrated in Figure it:

With the above principles in d one can reaclily follow the developmentoi the derivative circuit which follows. With an arrangement of elementssuch as is illustrated in 1H.- 17, by impressing a given E acrom the'circuit at the points i and 2, a, current I will flow through thecircuit. The value-oi this current will be equal to on. a? and alsoequal to so *2.

This relationship can be illustrated as shown in Figure 18. Now it thecapacitance and resistence are both made smell, so that, at thefrequcncies encountered, the voltage drop across (I isfar greater thanacross R, then a condition is reached where the current is leading thevolt age substantially 90 degrees substantially proportional to thederivative es the applied to voltage E. This is" illustrated in Figure19.

Therefore, a small component of voltage across the resistance R isohtalhod that is substantially proportional to the derivative of theimpressed voltage E. This component of voltage isolitaihed at theterminals 3 'd 63. Then by connecting across the terminal's't and tonother condenser Cs and resistance lite, as shown in Figure 38', asecond circuit by in of which the second --derlve.tive can be taken' isobtained.

The voltage measured at the points 5 and 6 across R2 is substantiallypro derivative of the voltage meas and 6 across R1, which voltaglstantially proportional to -thevoltage impressed at the termh Byaddingmore derivative this same manner any desired 1 tives can be takenelectrically t.

to produce a definite time-lore circuit embodying this inventio:

as six derlvating stages has he erated successfully.

The manner of sharpening e the kind involved in producing dication, bytaking derivatives 1: break definite is illustrated by inFigure 8. Thecurve marker original function and F, F", F resent the first, second,third, 2 tives, respectively.

In Figure 21 there is shown blaster circuit with that porti detonatesthe explosives, and i: by the shot firer, separated by the portion whichis carried as corder. The broken lines re; conductors which may be of adependent upon the distance where the explosive is detonat recorded. Inthis-figure con are given conventional identify is connected in serieswith a S( a switch 8. an iron core indul and a resistance R3. The ell orcaps are connected in pal slsltance R3. The resistance, 1

ample, about ohms, that 1 firing leads about 5 ohms. Tl be chosen atabout the value c purpose of limiting the electril the derivatlngcircuit consistir Ca and the resistance R4. The 11' voltage, in thismanner, isi magnitude to the time-break. ficient voltage from;the surgpreciable cross-feeding to the figures as stated above, of co kind andtype of blasting devl the caps. They are illustrai blasters, forexample, if R3 Lililil ohms, the time-break relatively large, and thetimeto the other traces would like cult described thus far is allactually detonate the blasti switch S .is closed. However the instant ofdetonation a struin'ent, which is normally mote point, some means 0:signal of necessity must be 1 ally. the present invention 111 ther, asshown in Figure ed ratio winding may be dependent upon the conispreferred to employ a of this electrostatically e then connected toconoken lines in Figure 21, ah the recording unit of ;he signal on itsway to meter G can, if desired, or more additional deid derlvatlng stagecon- C and the resistance Rt voltage across R5, which ivetive, is thenimpressed second electrostatlcally a of the same type and er tops of theprimary her to complete the pri e functions of this trans= out discussedin connecdormer; namely, to pre- 2 signal which has been aecohdery isthen conble resistance R3 to the meter element G. The looted can be usedot the ome manner as the .re-= .multlple element. gelwhich isillustrated, to a generated by the secl and in sympathy with. amplitudeby the amplb esietauce Re is used to l the time break and is utilized aso telephone adding a means of comrecorder and shot firer. to 6 acrossthe condenser the circuit and inserting me conductor ll, near themmunicotion can be es-- :ohdenserc ecross these e to its abnormally highlgh the condensers within amplitude. The nectentiel is placed on themeeting a battery B in the telephone. An am- 1 characteristics may be ebattery for purpose of lirect current in the telemce R2 of suitable size:1 Figure 21 in order to st circuit for the teleruoplete operativesystem 2 21, in additionto the ellthe twounitsof the mplifier J. amaster connere tcr and its amplifier water is usually an elecis utilizedto generate redetermlued frequency. fled drives a timing dewe recordedon a sensig film.- transverse lines smell intervals of ti c.

this character consl erable difllculty has been encountered due to thepresence of cross-feeding, which is caused by electrostatic couplingbetween adjacent circuits, the lack of properly proportloning thevoltages generated by speech modulations to those of timebreal:modulations, and stray currents which may be picked up from externalsources, such as high tension power lines adjacent to the recordinginstrument. In the circuit of this invention these dlmculties areovercome by grounding the primary center tops on the electrostatlcallyshield-= ed transformers T1 and T2, as shown in Figures 26 and 27. Insome cases to produce the best results it is found desirable to connectthe grounded center taps to a ground which actually extends out of theunit and contacts the earth's surface. Although this is desirable insome cases, in others, good results. are produced without this ground.

The iron core inductance or choke L1 in the circuit illustrated inFigure 26 serves athreefold purpose. The most important of these being,that it causes the current through the electric blasting cap or caps tobuild up to its maximum value at a relatively slow rate,thereby'insuring no lag in detonation after the bridge wire in the capis fused.

B'y referring to the cap-lag curves illustrated in Figure 22, it is seenthat if the bridge wire fuses in a. short time, the time necessary forthe cap to fire is substantially longer than that required for thebridge wire to fuse; Whereas, if the current is allowed to build upthrough the cap over a, long period of time, the period between thefusing of the bridge wire and the detonation of the cap disappears orbecomes very short and negligible. Therefore, the importance of the useof the iron core inductance or choke L1 becomes apparent.

Another function of this iron core inductance or choke L1 is to preventany false time-breaks from appearing on the record ahead of the realtime-break which occurs when the cap fires. Since in seismograph workone is dealing with thousandths of a. second, it is necessary that theseartificial time breaks which tend to confuse the interpreter beeliminated from the record.

The third function of this iron core inductance or choke L1 is ofextreme importance in geophystcal work. It serves to block outcommutator ripple so that there is no evidence of it on the selsmogram.Figure 23 illustrates a record which has been recorded without theironcore in- I ductance in the circuit. In this record one will observe thatthe commutator ripple generated by the deceleration of the blastinggenerator is so bad and of such great amplitude that it might beimpossible to determine the exact instant at which the first impulse ofenergy of an incoming seismic wave train was recorded on this trace.-Figures 24 and 25 show illustrations of actual records which wererecorded while the iron core inductance was in the circuit. It will benotedthat there is no commutator ripple and that flrst impulses'fromseismic waves can be identified on the trace carrying the time-break aseasily as on those which are not connected to the blasting circuit.

Although this invention has been described in detail as applicable; to acircuit utilizing the plunger'or generator type blaster, it is equallyapplicable when the plunger or generator type blaster has'beeu replacedby a battery; condenser bank, or transformer as a source of energy. Theonly change necessary to employ these other sources of power beingmerely thev substitution of one for the other.

The method of operation of this circuit can best be understoodwhendescribed inconnection with the circuit diagram shown in Figure 21. Acap or a plurality of caps are first connected as shown in the diagram.Then. after the shot firer has established by telephonic communicationwith the recorder that everything is in readiness' to record the seismicwaves when generated by the explosion, the cap or caps are then fired.If a plunger or generator type blaster is used, the shot firer raisesthe plunger and forces it downwardly thereby accelerating the generatorto a speed which will produce the desired voltage. Just before theplunger reaches the bottom of its stroke the switch S is automaticallyclosed, completing the circuit through the cap or caps and the choke L1.Due to the function of the choke, the current will build up slowlythrough the cap line until the cap bridge wire fuses enabling thedetonation of the cap to take place at substantially the same instantthat the wire bridge, fuses. Since the resistance of the cap or caps 5is relatively low as compared to that of R3, a very small portion of thecurrent will pass through R3, while the cap circuit is complete. But atthe time this circuit is ruptured by the fusing of the bridge wire inthe cap a potential 0 pulse is impressed across the resistance R3. Sincethe condenser C3 and resistance R4 which comprises the first derivatingstage is in parallel with R3, the same voltage impressed across R3 willin like manner be derivating stage. The condenser C3 and resistance R;will then function to take the derivative of this voltage electrically.If the primary of an electrostatically shielded transformer be connectedacross the resistance R4, as shown, this 40 derivative of the originalhigh frequency surge of current will be transformed to the secondary ofthe transformer, The outer terminals of the tapped secondary winding areconnected to the conductors Y which communicate with the recording endof the system, and this voltage then,

which is a derivative of the original high frequency surge, will beimpressed across the resistance R1. Since the condenser C4 is connectedin series with the resistance R5 and the series combination, comprisinga second derivating stage, is in parallel with R1, then the voltagesurge which is the derivative of the original surge will have its secondderivative taken electrically. Then, by connecting the primary of thesecond electrostatically shielded transformer-Ta across the resistanceR5, this same voltage which is the derivative of the derivative of theoriginal high frequency surge, will be transformed to the secondary ofthe transformer. By connecting the outer leads of this tapped secondarythrough a variable resistance Re to the vibrating element of agalvanometer this'signal, which is in reality an indication of the timeof detonation of the explosion which generated the seismic waves to berecorded, is impressed across. the galvanometer element and will actuateit to record on the seismogram a definite time at which the explosionwas detonated.

As previously described, due to the fact that the circuit is balanced bygrounding the cen- 7o tral taps of the primary windings of thetransformers, the voltages generated by voice modulations are soproportioned to those generated by the time break signal modulationsthat 'none of will be carried 5 the voice modulation voltages impressedacross the through the circuit to the recording Therefore, anydisturbance such shouting into the telephone or vibi are generated bythe wind blowing phone would not in any way distur ing element. Thisfeature makes use the same galvanometer element time-break signal isrecorded 1 seismic waves.

The condensers Ca and C4, in ad( ing as elements of the derivating s asafeguard against premature det cap or caps byany direct curren used inthe system, such for exam phone communications. -With the present in thecircuit, it is apparen cuit can-be used with safety um other than thosewhere a perfectly tem is desired.

,1 claim:

1. In combination with an electri an electric circuit for detonating ecaps comprising in combination energy, common means for retard which thecurrent is built up in and eliminating spurious voltage: mutator ripplevoltages from th cuit, electric derivating means for rivativeelectrically of a transient ing means, and signal commul connecting saidblasting-circuit ti means, whereby a definite indict stant of detonationof the cap m 2. In combination with an elect] a blasting circuit, saidblasting oil a source of voltage, a switch, a ductance and a resistancecan: a pair of leads whereby an elect can be connected in parallel withderivating means also connected the resistance comprising a conderesistance connected in series, a 1; ing its primary winding conne withthe second resistance, a 1 nometer, signal communicating ing thesecondary of said transi galvanometer whereby a signal blasting circuitat the time ofc' cap may be derivated, transmit1 nometer and recorded.

3. In combination with an elec a blasting circuit, said circuit cobination a source of electric ene an electric blasting cap connectsistance connected in parallel i cap, derivatlng means connecte saidresistance and electric b derivating-means comprising a resistanceconnected in serie having its primary winding cor with said derivatingresistance, nometer, and a signal communi necting the secondary of saidthe recording galvanometer, w voltage produced at the time the electricblasting cap w derivated and transformed t munication circuit andrecorde by the recording galvanomete 4. In an electrical seismogr. avacuum tube amplifier, a nected to the input of said a1 connected totheoutput of s: timing means associated with adapted to cooperate withsa areaaaa an electric blasting circuit splosive, said circuitcomprisirating a transient voltage in instant of detonation of the ctriccircuit adapted to trans- F said voltage to a recorder, at compriseselectrical derivai said signal transmitting cirat least one derivativeof said to distort said voltage and rent thereof more abrupt inseismograph system having" a ier, a seisnp meter connected d amplifier,a recorder con.-

nected to the output of said amplifier and a timing means associatedwith said recorder and adapted in said signal transmitting circuitadapted to take a plurality of derivatives of said transient voltage todistort said voltage and render the wave front thereof more abrupt incharacter.

